Hello I think using UNIQUE is the way to go simply because of data integrety (<= how do you spell this??? ; ) ) If you don't use UNIQUE and you are not write locking your table you might accidently get duplicate Values. UNIQUE is the only way to prevent duplicate data without a lot of hassle. This doesn't mean you cannot check upon duplicates first, which I think is obsolete since you need to add error checking code anyway.
Regards Stefan Langer